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otation and 19 had a paradoxical tibial external rotation.DISCUSSION: It is possible to record the kinematic behavior of a knee intra-operatively duringtotal knee replacement. This might help choosing the most appropriate type of reconstruction toget a closer to a normal kinematic. The surgeon might for example test different posterior tibialslopes, different heights of polyethylene inlays, different rotational position of the tibialcomponent… However, only passive kinematic may be analyzed, and it might be significantlydifferent from the active kinematic after the procedure. Furthermore, this software allows akinematic registration of the antero-posterior stability, which is not commonly displayed byusual navigation system. This may help choosing between preservation or substitution of theposterior cruciate ligament.Poster: 21Accuracy of CT Based Navigation System for Acetabular ComponentPlacement in Cementless Total Hip Arthroplasty*Hiroshi Egawa - Tokushima University - Tokushima City, JapanNatsuo Yasui - Tokushima - Tokushima, Japan*Email: egawah@gmail.comIntroduction: Proper positioning of the acetabular component in total hip arthroplasty (THA) isessential regarding the short-term success and longevity. Improper cup placement may lead todislocation, accelerated polyethylene wear associated with periprosthetic osteolysis, andcomponent loosening. Because of substantial errors of manual technique in cup placement evenwith experienced surgeon, computer aided navigation system has been developed in recentyears. The advantage of applying navigation system is enhanced especially when we operate inthe lateral decubitus position, which may precipitate misjudgment in estimation of pelvicorientation. The purpose of this study was to evaluate how accurate we were able to placecementless cups with CT based navigation system compared with the conventional mechanicalguiding instruments.Materials and Methods: Sixty patients who underwent cementless total hip arthroplasty withCT based navigation system (Stryker Japan) were employed for this study. The average age ofthe patients at the time of surgery was 63.9 years (range, 30-84 years, 9 men and 51 women).We implanted cementless hemispherical TriAD cups (Stryker Japan) using direct lateralapproach in lateral decubitus position. For all the patients, post-operative CT scans wereperformed and the cup inclination and anteversion angle were measured using 3D imageprocessingsoftware (Stryker, Japan). Control group included 30 patients who underwent THAwith the conventional mechanical guiding instruments, using same implant and surgicalexposure. The difference between the intra-operative target angle and the angle measured fromthe post-operative CT image were calculated and the accuracy was compared between thenavigated and conventional groups.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]